Answer / ss

because using higher frequency makes the trnsfrmr size small.

Answer / raina

400 hz is used in aircraft because this is the optimum
frequency. If frequency more than 400 hz used losses will
increase since most of losses increase with increase in
frequency and if lower frequency is used than size of the
component will increase.so 400 hz is the optimum frequncy
which provide the balance i.e. for the given size of
component or equipment losses is not that much high.

Answer / ravi

Higher than usual frequencies, such as 400 Hz, offer
several advantages over 60 Hz – notably in allowing
smaller, lighter power supplies to be used for military
hardware, commercial aircraft operations and computer
applications. As aircraft space is at a premium and weight
is critical to aircraft engine thrust and fuel burn (and
thus the aircraft range and engine horsepower per pound),
115 volts at 400 Hz offers a distinct advantage and is much
better than the usual 60 Hz used in utility power generation

Answer / ashish yadav

IN A AITCRAFT SPACE SAVING IS IMPORTANT, BY USING A 400 HZ FREQ THE SIZE OF MOTOR, GENERATOR, ALTERNATOR & TRANSFORMER SIZE CAN REDUCED BECAUSE SPEED IS DIRECTLY PROPORTIONAL TO FREQ AND INVERSELY PROPORTIONAL TO FLUX THERFORE FLUX IS INVER TO FREQ.HIGHER THE FREQ LESSER THE FLUX AND LESSER THE CORE SIZE MEANS LESS WEIGHT AND SIZE.
ALSO 400 HZ IS A CRITICAL FREQ ABOVE WHICH CONDUCTOR SHOW SKIN EFFECT MEANS START RADIATING, THIS AFFECT THE RADIO SYSTEM PERFORMANCE.

Answer / m.venkatesh

1. noise(EMI) reduction
2. component size reduction
3. space and weight reduction

Answer / rajavel.k

Aircraft electrical components operate on many
different voltages, but most aircraft systems use
115 volts AC at 400 Hz or 28 volts DC. 400 Hz
offers several advantages over 50/60 Hz, namely
by allowing smaller, lighter power supplies to be
used for military hardware, commercial aircraft
operations and computer applications. Reducing
the space and weight requirements of electronic
equipment improve aircraft thrust and fuel burn.
Along with the higher frequency and advantages of
the 400 Hz system comes more sensitivity to voltage
drop problems—both resistive and reactive. Thus,
in order to properly test and monitor the
performance of aviation power systems.

Answer / mahesh

It is mainly to reduce the size of the electrical equipment.
As, flux is inversely proportional to speed(frequency). so
as freqwuency increases, flux reduces. thus the core size
gets reduced.

Answer / guest

because using higher frequency makes the trnsfrmr size small.

Answer / adrin

As aircraft fly higher, faster and grow larger, the services
that the power supply has to satisfy also grow more complex.
In civil aircraft this means more power to the galley units,
environmental control and passenger entertainment systems,
while military aircraft require more power sensors and
weapon systems. Both have increased power demands for
actuators, lighting systems, avionics and heating.

There are several different power sources on aircraft to
power the aircraft electrical systems. These power sources
include: engine driven AC generators, auxiliary power units
(APUs), external power and ram air turbines.

The primary function of an aircraft electrical system is to
generate, regulate and distribute electrical power
throughout the aircraft. The aircraft electrical power
system is used to operate (a) aircraft flight instruments,
(b) essential systems such as anti-icing etc. and (c)
passenger services. Essential power is power that the
aircraft needs to be able to continue safe operation.
Passenger services power is the power that is used for cabin
lighting, operation of entertainment systems and preparation
of food.

Aircraft electrical components operate on many different
voltages both AC and DC. However, most of the aircraft
systems use 115 volts (V) AC at 400 hertz (Hz) or 28 volts
DC. 26 volts AC is also used in some aircraft for lighting
purposes. DC power is generally provided by “self-exciting”
generators containing electromagnetics, where the power is
generated by a commutator which regulates the output voltage
of 28 volts DC. AC power, normally at a phase voltage of
115 V, is generated by an alternator, generally in a
three-phase system and at a frequency of 400 Hz.

Higher than usual frequencies, such as 400 Hz, offer several
advantages over 60 Hz – notably in allowing smaller, lighter
power supplies to be used for military hardware, commercial
aircraft operations and computer applications. As aircraft
space is at a premium and weight is critical to aircraft
engine thrust and fuel burn (and thus the aircraft range and
engine horsepower per pound), 115 volts at 400 Hz offers a
distinct advantage and is much better than the usual 60 Hz
used in utility power generation.

However, higher frequencies are also more sensitive to
voltage drop problems. There are two types of drops:
resistive and reactive. Resistive losses are a function of
current flowing through a conductor with respect to the
length and size of the conductor. This is the most
important factor in controlling resistive power loss and
applies regardless of frequency. The short transmission
range of higher frequencies is not a factor in most airborne
applications.

Reactive drops, on the other hand, are caused by the
inductive properties of the conductor. Reactive drops are a
function of both cable length and the AC frequency flowing
through the conductor. With high frequencies such as 400 Hz,
reactive drops are up to seven times greater at 60 Hz.

This raises an interesting question: can you run a 400 Hz
device at 60 Hz.? If you try this, smoke and fire are
certain to result. The lower winding inductance draws a much
higher current at a set voltage, saturates the iron, and
burns up. However, there is a simple workaround using
fundamental principles of flux density. A 400 Hz device will
usually run just fine on 60 Hz if you lower the voltage to
60/400ths or 0.15. The same current will produce the same
magnetic flux, and the device will operate happily.

Answer / shamas ul hasan

Transformers, for example, can be made smaller because the magnetic core can be much smaller for the same voltage level. Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships.
A United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.

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